Preheat the oven to 300° F. Line a small baking sheet with parchment paper.
Slice the lemon half into ¼-inch thick slices and lay them on the baking sheet. Brush the lemon slices with a little maple syrup.
Roast the lemon slices for about 45 minutes, until they are browned and no longer juicy. Remove them from the oven and let them cool.
Note: this step can be done in advance. Store the cooled slices in a sealed container in the fridge for up to two days.
Make the drink:
Divide the remaining maple syrup between two heat-proof glasses, mugs, or small mason jars. Divide the gin and the lemon juice between the two cups as well.
Pour the hot water into the cups, about ¾ cup into each one. Stir each drink to mix the gin, water and flavorings together.
Cut a small slit into each of the roasted lemon slices. Add one or two lemon slices to each rim. Serve the hot toddies immediately.